Tiny short travel switches are available, which may include a small snapdome whose middle can be depressed until the snapdome snaps past center and contacts a terminal. U.S. Pat. No. 3,967,084 shows one example of this type of switch. The total travel of a button lying against the snapdome may be 15 mil (one mil equals one thousandth inch). The availability of such low cost small travel switches has the potential to reduce the cost of push-button switches. However, one type of commonly used push-button switch has a long travel such as about 3/16ths inch (187 mil), with the force opposing depression increasing gradually, such as is obtained with a single spring. In order to enable acceptance of low cost push-button switches using the low cost short travel switches, it is desirable to construct the push-button switches so they have the same long stroke, smooth action, as present common push button assemblies.
One prior art push-button switch using a short travel switch is shown in U.S. Pat. No. 4,156,802. That patent describes a switch assembly which uses two springs in parallel. As the push button is depressed, only a first or key spring is initially deflected until the plunger makes contact with the short travel switch. The required load on the push button increases greatly until the preload of the second or follower spring is overcome and the follower spring begins to deflect. When the push button load is sufficient, it operates the short travel switch and the push button can be deflected a short distance thereafter. The large increase in force between complete compression of the key spring and the beginning of deflection of the follower spring provides a false tactile feedback indicating that the short travel switch has been operated. Also, the push button does not have a substantially continuous smooth increase in force as the push button is deflected, to mimic the single spring switch that is presently commonly used.
Where the push-button switch is to be illuminated, as by a lamp immediately under the push button, a low cost but reliable electrical connection is required between the lamp at the middle of the housing around which the plunger moves, and the outside of the housing where current is applied. A low cost but reliable switch assembly based upon a short travel switch, which provided characteristics mimicking those of presently available push-button switches, and which enabled the push button to be illuminated by providing current to a lamp at the middle of the housing, in a low cost and reliable manner, would be of considerable value.